• Stage One: pre-Industrial Revolution, birth rates and death rates are both high, the level of the population stays the same
• Stage Two: in a developing country death rates tents to diminish while birth rates stay high: population is growing
• Stage Three: thanks to the better economic and living conditions, births starts to decrease
• Stage Four: birth rates and death rates are both low, so population is stabilizing. Most of today's developed countries are in this stage
• Stage Five (possible stage): here the birth rates have fallen below death rates, so the quantity of older people is bigger than the quantity of younger ones

Logistic model for Population Growth:

\[ \frac{dN}{dt} = rN(1-\frac{N}{K}) \] It can be integrated, obtaining:

\[ N(t) = \frac{K N_0 e^{-rt}}{K + N_0(e^{-rt}-1)} \]

Where \(N_0\) is the starting number of individuals.